1. Field of the Invention
The present invention generally relates to a graphic control system for controlling motion of a computer graphics (CG) model that has a skeleton structure generated by computer graphics and that is adapted to be operated for presenting various postures of the model.
2. Description of Related Art
In order to impart a sequence of motions to a CG model or an object having a skeleton structure of a human body or an animal body for example, it is required to specify a change in an articular angle and a positional shift of joints or articular segments of the skeleton structure. Conventionally, this specification has been performed by use of a motion capture device. This device controls a CG model based on data obtained from sensors attached to a source moving body to capture motions thereof. The method used by this device is advantageous in that a multiple of control points or joints can be handled by use of a multiple of sensors. In addition, if sensors can be arranged in configuration generally simulating an object to be displayed, appreciably realistic motions can be imparted to the object of a human body for example. However, this motion capture device has drawbacks in that the device itself is very large in scale and lots of operations are required for controlling a CG model.
In consideration of the above-mentioned drawbacks, a system has been developed in which an input glove is used for a simplified input device to edit an animation in real-time by three-dimensional CG (hereafter referred to as 3D CG). The input glove is worn by a hand of the operator to detect movements of fingers, by which a computer is controlled. For example, such a system is disclosed in "Development and Operation of a Real-time Character Animation System," Ogura, NICOGRAPH Collected Papers, 1993, pp. 131-139. In the disclosed system, control units arranged on joints of each finger of the input glove are assigned to joints or articular elements of a 3D CG object so that the motion thereof is controlled as if manipulating a puppet.
However, the above-mentioned real-time character animation system is intended to move a CG model in real-time while superimposing the same on a video taken from life. In this system, only simple operation is conducted by the input glove. The conventional input glove is not designed to handle complicated motions of CG model as with motion capture device. Therefore, CG model motions are confined to simple ones, thereby narrowing an application field. Another problem is that no consideration is taken into editing of recorded motions of CG model.
As described before, in order to impart a sequence of motions to a CG model having a skeleton structure of a human body or an animal for example, it is required to specify a change in the angle and position of joints contained in the skeleton structure. The location of the CG model is determined by three-dimensional coordinates of a parent or basic joint. Normally, the parent joint is often set to the waist or the pelvis of the CG model. Therefore, if both knees of the CG model are bent with no preparatory process performed, the CG mode floats in the air, which is an unnatural state or posture. To prevent this problem from occurring, the foot position of the CG model is specified beforehand on the reference plane (namely, the floor) of a virtual space, and motions of the feet are determined by functional approximation or the like, based on which the position of the CG model is determined by use of a method such as inverse cinema. However, because the above-mentioned method requires a high computational complexity, it is difficult to control a CG model real-time. The above-mentioned method also needs to determine the foot position beforehand, thereby making it difficult to freely move a CG model real-time by use of an external controller for example.